While results from the RV144 vaccine efficacy trial were encouraging, protection was modest and not sustained. An emerging picture of desirable characteristics of candidate HIV vaccines include one that induces a sustained response that includes broadly neutralizing antibodies (bnAbs), non- neutralizing antibodies including those that mediate ADCC as well as strong virus-specific memory T cells. Results from attenuated virus studies, CMV-vectored SIV/HIV vaccines and analysis of antibody maturation over time all suggest that ongoing viral antigen expression may be an essential component to drive a mature and broad response. Integrase defective lentiviral vectors (IDLV) engineered with safety features that prevent integration and replication result in prolonged antigen expression with robust and sustained T and B cell responses in mice and non-human primates (NHP). This Program Project Grant combines the unique features of IDLV with recent immunogen design strategies aimed at promoting maturation of an effective immune response over time and will be studied in the NHP model. IDLV will be engineered to express a series of Envelope immunogens based on the recently described CH505 transmitted/founder envelope and a series of subsequent variants derived from an individual that developed CD4-binding site bnAbs. An administrative core (Core A) will assure that the proposed scientific plan is effectively carried ot and an NHP core (Core B) which will oversee two NHP protocols and perform quantitative and qualitative T cell assays in support of two projects. Project 1 will develop and validate IDLV engineered to express the Env immunogens and will define the mechanisms that uniquely sustain antigen expression. In vitro and in vivo testing will determine vector and expression durability, integration state and ability to mobilize vector-based virus. Project 2 will determine he systemic and mucosal B cell responses including neutralization and ADCC (against bnAb-associated epitopes) and isolate and characterize monoclonal antibodies over time two vaccine arms. These studies will test the hypothesis that persistent expression of strategically chosen envelopes will lead to maturation and broadening to an effective immune response.